Predation by Common Ravens (Corvus corax) on Eggs of Rhinoceros Auklets (Cerorhinca monocerata) and Kleptoparasitism by Bald Eagles (Haliaeetus leucocephalus)

Abstract

ABSTRACT We recently reported observations of Common Ravens (Corvus corax) eating eggs, juveniles, and possibly adult Rhinoceros Auklets (Cerorhinca monocerata) on Protection Island National Wildlife Refuge, Jefferson County, Washington. In this new report from 2015, we found 32 eggs presumably eaten by ravens, which represents a 16-fold increase during the same time window of the breeding season of 2014. In addition, we report on one attempted and one observed kleptoparasitism (food piracy) event by Bald Eagles (Haliaeetus leucocephalus). An adult eagle was observed chasing a raven carrying a recently caught egg in its mandibles. In a second instance, an immature eagle stole and ate an egg that was being eaten by a raven. It is currently unknown if the combination of increased feeding by Common Ravens on Rhinoceros Auklets, and kleptoparasitism by Bald Eagles stealing recently captured auklet eggs from ravens influences predation pressure on the auklet colony at Protection Island.